Effect of PH3 poisoning on a Ni-YSZ anode-supported solid oxide fuel cell under various operating conditions

The Ni-YSZ anode-supported solid oxide fuel cell (SOFC) can generate electrical power by using coal-derived syngas as the fuel. However, trace contamination of phosphine (PH3) in the syngas can cause irreversible degradation in cell performance. A series of tests at 10 ppm PH3 in the fuel gas was carried out under a variety of operating conditions, viz, with/without electrochemical reaction in syngas and with/without H2O in H2 fuel at 750 °C, 800 °C and 850 °C. The poisoning effects were evaluated by both electrochemical methods and chemical analyses. The post-mortem analyses of the SOFC anode were performed by means of XRD, SEM/EDS, and XPS. The results show that the degradation rate is larger at the higher cell working temperature using syngas with PH3 in a 200 h test though PH3 is more reactive with Ni in the anode at lower working temperature and produces a secondary nickel phosphide (NixPy) phase. The dominant compositions of NixPy on the cell anode are Ni5P2 with the presence of H2O, and Ni12P5 without the presence of H2O. The production of NixPy can be generated on the cell anode using syngas or dry H2 fuel with 10 ppm PH3 contaminant. Further, the appearance of NixPy phases is independent of the electrochemical reactions in the cell.